Water soluble alchols having more than one carbon atom are utilized in many industrial processes where they often become combined with water thus forming aqueous-alcohol mixtures. For most such industrial processes, it is necessary to recover the alcohol if utilization of the process is to be economically feasible. Processes for the manufacture of carboxymethyl cellulose (CMC) and other cellulose derivatives often utilize water soluble alcohols; such processes will be used herein to illustrate the process of the present invention; however, the present invention is not limited to such processes.
The most common process used to recover water soluble alcohols from aqueous-alcohol mixtures is distillation. Many of the water soluble alcohols form azeotropic mixtures with water and cannot be completely dehydrated by simple binary distillation techniques. Even where substantial dehydration of alcohol-water mixtures can be achieved by distillation, distillation has a disadvantage of requiring high energy input in order to achieve the separation. Also, a distillation process requires substantial startup and shutdown times to bring the system to equilibrium conditions so that the desired separation of components is achieved. The loss of 1-2% or more of the alcohol being recovered by distillation is common.
It is known that dehydration of certain water soluble alcohols can be achieved by the addition of a base or an electrolyte to an aqueous-alcohol mixture to cause separation of the mixture into two immiscible layers, the upper layer of which is alcohol-rich. U.S. Pat. No. 1,452,206 issued to Mann on Apr. 17, 1923, discloses the dehydration of higher alcohols, that is, of alcohols containing three or more carbon atoms, especially isopropyl alcohol (IPA), by the addition of caustic alkali such as sodium hydroxide or potassium hydroxide to cause the formation of two immiscible layers, the upper layer being alcohol-rich. Similar dehydration processes are disclosed in U.S. Pat. No. 2,461,048 issued to Frejacques on Feb. 8, 1949, for normal propyl alcohol and isopropyl by the addition of ammonium carbonate; and by U.S. Pat. No. 2,534,259 issued to Gee & Bossche on Dec. 19, 1950, for ethanol by the addition of aluminum sulfate. However, such processes have not often been used in industrial applications due to the cost of the chemicals required, or the impurities introduced into the recovered alcohol.
Information concerning the equilibrium of IPA-water-salt mixtures for many different salts is presented in Ginnings, P. M., and Z. T. Chen, "Ternary Systems: Water, Isopropanol and Salts at 25.degree., " Journal of American Chemical Society, Vol. 53, pages 3765-9 (1931); and Steven, H. (ed.), Solubilities of Inorganic and Organic Compounds, Vol. 2, Part 1, pages 105, 128, and 146.